1. Field of the Invention
The present invention relates to a method of manufacturing water-in-oil emulsion explosives which are sensitive to blasting cap initiation. By the term "sensitive to blasting cap initiation" is meant that the explosives may be detonated by a conventional No. 8 detonator.
2. Description of the Prior Art
Water-in-oil emulsion explosives are well known in the explosives art and have been demonstrated to be safe, economic and simple to manufacture and to yield excellent blasting results. Bluhm, in U.S. Pat. No. 3,447,978, disclose the first practical emulsion explosive composition which comprised an aqueous discontinuous phase containing dissolved oxygen-supplying salts, a carbonaceous fuel continuous phase, an occluded gas and an emulsifier. Since Bluhm, further disclosures have described improvements and variations in water-in-oil emulsion compositions. These types of explosives are prepared by emulsifying an organic oxidizer salt which has been dissolved in water with a liquid carbonaceous fuel in the presence of an emulsifying agent. The compositions are commonly sensitized by the incorporation therein of small gas bubbles or by including gas entrapping material. The incorporation of gas bubbles by the in situ chemical generation of gas in the emulsion as a result of the decomposition of a chemical therein is described in, for example, U.S. Pat. Nos. 3,706,607, 3,711,345 and 3,790,415. Generally, the foaming agent is added to the emulsified mixture of the other ingredients, the composition being sufficiently viscous to entrap the gas bubbles when they are generated. U.S. Pat. No. 4,008,180 describes a method of chemically foaming an emulsion explosive by continuously injecting a gas generated material into a stream of the emulsion and thereafter delivering the stream into one or more packaging receivers. The gas generating material thereafter reacts to evolve gas so as to foam the emulsion in the package.
This method, like other similar methods wherein the gas generating chemical is distributed throughout the explosive emulsion by mixing or similar means, is not without disadvantage. In order to achieve wide distribution of the gassing agent, it is essential that the mixing procedure results in a breaking-up of the chemical gassing agent into small particles and distributing these particles throughout the emulsion explosive mass. Since such mixing procedure results in a substantial random distribution of the chemical gassing agent throughout the emulsion, there may be volumes of the emulsion wherein no gassing has occurred. Without adequate distribution of the gas generating material and the gas bubbles provided thereby, the explosive may lack cap sensitivity. In an effort to improve the distribution of the chemical gassing agent, it has been proposed in published South African patent specification No. 85/3253, that a two-component chemical gassing system be employed. In this proposed system, one reactive component is admixed with the carbonaceous fuel phase and a second reactive component is mixed with the aqueous salt phase. The subsequent emulsification of the carbonaceous fuel phase and the aqueous salt phase thereby produced a widely distributed system of gas bubbles throughout the emulsified composition. While this proposal is meritorious, it requires careful control of the amount of the two reactive components in each of the two phases of the emulsion. Furthermore, to achieve suitable distribution of very fine gas bubbles throughout the emulsion, it is necessary that very fine particles of the two reactive components combine at sites distributed throughout the mass.